[onsk (OP)]

I have read different sets of instructions on how one should treat mobile computer batteries if one wants to keep them in good shape for as long as possible. Some warn that leaving them in the computer while it runs on electricity from the grid may harm them. Other claim that modern batteries have circuits protecting them against the damages of overcharging. Some say that batteries should better be used until empty before recharging them, whereas others claim they should be charged whenever possible.

So what is the truth? Is it a good idea to leave the battery attached to the computer while it is using electricity from the grid, and while connected to the mains but not operating? Is it better to disconnect the computer when not in use to avoid overcharging the battery, or is the battery protected? Should I try to use the battery until it is almost empty before I recharge it, or should I better charge it whenever I have a chance to do so even if it is far from empty?

An explanation of the physics of the mechanism would be appreciated.

[LeeE]

Leaving the battery in my old PIII Vaio laptop while it was constantly running on the mains did indeed kill the battery.  It seems that Li batteries have a very high value resistor across the terminals to ensure that they will continue to discharge at a very slow rate even when not in use.  When the LT is running off of the mains then, the battery is still discharging, and when the LT notices that the battery charge level has dropped below a certain threshold it'll start to charge it again.  The result is that the battery can get through lots of recharge cycles without you being aware of it, and usually when there's only been a tiny drop in the charge level of the battery.

Newer systems may not do this, but I wouldn't risk it; if I know the LT isn't going to need the battery for a long time I'd take it out, or conversely, I'd run it on batteries until it needs charging, and only then plug it in.

[onsk (OP)]

Thanks. That makes sense.

[SeanB]

Most modern laptop battery chargers keep the battery conditioned very well, but the battery is constantly exposed to high temperatures inside the laptop. This shortens the battery life, as the design life is measured and tested on the pre production samples and QC samples whilst they are maintained at 25 degrees C in the test area. Lithium batteries are best when not deeply discharged, and kept cool and near full charge with short discharge cycles.

The high temperature inside the laptop is what leads to accelerated wear on the cells, and can lead to the extreme of the flaming battery death, although this is often caused by improper charging, either via a pirate or faulty charger, or by using an improperly designed battery pack or a poorly manufactured battery.

Many laptops can operate without the battery pack, although some will throttle back to a low power mode ( Macbooks especially) when the battery is not present. You do lose the important advantage of having a built in UPS doing so, but it can be sone.

[techmind]

From what I understand (and I looked into this to assessthe performance issues with Li-Ion for a handheld medical device), there are several issues to contend with...

Permanent loss of capacity can occur partly as a function of cycling (charge/discharge cycles) but also as a function of time. A Li-Ion battery degrades to a significant extent purely sitting around doing nothing. This self-degradation over time is worst as elevated temperatures and when near fully-charged. A laptop which keeps the battery topped-up, and warm, is therefore a bad case.

See table 1 on this page for some examples: http://batteryuniversity.com/parttwo-34.htm

It is very important not to over-discharge Li-Ion as metallic lithium can form (fire/explosion hazard), and while normal electronic controllers will shut the equipment down before the battery is over-discharged, you don't want to store them discharged as they could then self-discharge over weeks/months to an overdischarged state.
New Li-Ion batteries are often supplied by the manufacturer at around 35-40% charged, low eneough that self-aging is slow, but high enough that they're unlikely to critically self-discharge before their first customer use.

[LeeE]

The high temperature inside the laptop is what leads to accelerated wear on the cells, and can lead to the extreme of the flaming battery death, although this is often caused by improper charging, either via a pirate or faulty charger, or by using an improperly designed battery pack or a poorly manufactured battery.

Many laptops can operate without the battery pack, although some will throttle back to a low power mode ( Macbooks especially) when the battery is not present. You do lose the important advantage of having a built in UPS doing so, but it can be sone.

The 'flaming' battery syndrom is almost entirely due to manufacturing defects; iirc the cause is shorting inside the battery, caused by the presence of fine metal particles in the dielectric.

I've yet to see a laptop that can't operate without it's battery and LTs may throttle their performance when running on batteries, not when they're running from an external supply.  The idea behind throttling performance, usually by reducing the clock speed, is to save power and increase the running time you'll get from a battery; why would you need to throttle performance when you're using an external power source?

[onsk (OP)]

Thanks for all the enlightening answers.